The present invention relates to a magneto-resistance element (MR element) utilizing magneto-resistance effect, and more particularly to the structure of a passivation film for protecting the MR element, together with a manufacturing method thereof.
MR elements are magnetic transducers utilizing the phenomenon that the electric resistance of a ferromagnetic magneto-resistance film varies with the relative intensity and direction of the magnetic field and, by virtue of their small size and high sensitivity, are extensively used as magnetic sensors and magnetic heads for playback use.
Silicon dioxide passivation films formed by any conventional method involves the following problems. First, after a ferromagnetic metal film and a silicon dioxide film are formed into the substrate film, much of its magnetic effect is lost, and the essentially expected characteristics of the MR element, especially its resistance variation rate, deteriorate during the manufacturing process.
Second, the product is susceptible to many defects due to pinholes and cracks in the passivation film, difficult to effectively protect from humidity, and unstable in electrical characteristics. As a result, the manufacturing yield is very low.
Third, the ferromagnetic metal film consisting of NiFe, Au and Cr gives rise to a level gap from the substrate surface. For this reason, in order to coat the gap part as well with the passivation film, a thickness of about 2 .mu.m is required for the passivation film. As a consequence, in the case of a conventional MR element shown in FIG. 1 for example, if the substrate 21 is coated with a passivation film 25 of 4 .mu.m, the parts near the sides of the ferromagnetic metal film 22 will be coated in a thickness of only about 0.5 .mu.m at most, resulting in a lack of uniformity. Moreover, a relatively thick and non-uniform film is susceptible to stresses, which might invite changes in the characteristics of the MR element.
An MR element embodying an attempt to solve the second and third among the above-mentioned problems is described in the Gazette of the Japanese Patent Laid-open No. 310186 of 1988. The idea is to reduce the film thickness and ease the stresses within the film by uniformly forming the silicon dioxide film by the use of plasma chemical vapor deposition (CVD). Regarding the first problem, however, even the cause is not identified, and the formation of the silicon dioxide film by plasma CVD is unable to solve the first problem.